Oxidation of hydrocarbons



Jan. 24, 1950 M. H. KOTZEBUE 2,495,332

OXIDATION OF HYDROCARBONS Filed Oct. 16, 1947 Asacmam ABSKIRBERv INVENTOR.

MEINHARD H. Ko-rz EBUE.

AT TORN EYS HYDROCAR 50H F B E D Patented Jan. 24, 1950 2.4 95,882 OXIDATION OF HYDROCABBONS Meinhard H.

Kotzebue, Houston, Tex, assignor to Celanese Corporation of America, a corporation of Delaware Application October 18, 1947, Serial No. 780,187 Claims. (Cl. 260-451) This invention relates to a process for the production of oxygenated organic compounds and relates more particularly to an improved process for the production of organic compounds by the oxygenation of hydrocarbons in a highly eflicient and economical manner.

In the partial oxidation of aromatic, cycioaiiphatic and aliphatic hydrocarbons. such as propane and butane, for example, at elevated temperature and pressure with the aid 01' a controlled amount of air, products such as acetaldehyde, formaldehyde, propionaldehyde, acetone, acetic acid and other organic compounds such as methyl, ethyl and propyl alcohol are produced. The use of elevated temperature and pressure unstable state, the cracked hydrocarbons combine with oxygen in an exothermic reaction. The oxygenated reaction mixture obtained normally contains some unreacted hydrocarbon since the amount oi air employed is limited to avoid the formation of lean mixtures low in hydrocarbon content. Such lean mixtures not only create a possible explosion hazard due to excessively rapid and uncontrollable temperature rise but also favor the complete oxi-- dation of the hydrocarbons to coke, resins and carbon dioxide rather than a limited oxidation to the desired oxygenated compounds. The unreacted hydrocarbon must, of course, be recovered and recycled in the process in order to render the same commercially feasible. However, recovery and recycling is costly since hydrocarbon recovery must be efl'ected under high pressures. Accordingly, eilecting the oxidation in a manner which produces as great a conversion of the hydrocarbons as possible to oxygenated organic compounds and, in addition, a reduction in the cost of the hydrocarbon recovery is obviously, a substantial step forward in the art.

It is, therefore, an important object of this invention to provide an improved process for e1- feeting the partial oxidation of hydrocarbons to form oxygenated organic compounds whereby said reaction is carried out in stages whereby the amount of hydrocarbon oxidized per pass to commercially valuable products is greatly increased.

Another object or this invention is to carry out said hydrocarbon oxygenation by simultaneously eiiecting a partial cracking or the hydrocarbons undergoing reaction.

A further object or this invention is the provision of a hydrocarbon oxygenation process wherein unreacted hydrocarbons are recovered under pressure in an economical and efllcient manner and substantially complete utilization 01' maintain the temperature at from about 600 to 900 F. and the secondary oxidation effected with oxygen at a temperature of about 900 to 1250 1?. followed by rapid cooling. The amount of oxy- The secondary oxidation not only acts to oxygenate part of the unreacted hydrocarbon but also acts simultaneously to further crack a part of the unreacted hydrocarbons present and thus render further oxygenation of the unreacted hydrocarbons to oxygenated compounds during this secondary oxidation more complete. The oxygenation reactions are preferably eiiected under pressures of to 200 pounds per square inch gauge, the pressure employed depending upon the particular hydrocarbon or hydrocarbon mixture undergoing oxidation and the type of oxygenated products desired.

The gaseous reaction products leaving the reaction zone following the secondary oxidation are immediately cooled to between about 300 to 500 F. to halt further reaction and the tars and resins present are then removed in a suitable scrubher. The scrubbed reaction gases are cooled further to between to 200 F., passed through a second scrubber where the high-boiling products are removed, and then passed through a water absorber to remove the water-solubl oxidation products such as aldehydes, acids, ketohes, etc. The gaseous portion which remains after the products are removed comprises cracked, aromatic or unsaturated hydrocarbons, light hydro unsaturated hydrocarbons are removed from the gases by being absorbed in a suitable solvent such as kerosene or mineral seal oil, preferably with some diethylene glycol present to remove any water vapor. These hydrocarbons may stripped from the solvent and recycled to the system in whole or in part or subjected to a separate. further oxygenation. The remaining gaseous mixture comprises the valuable unreacted light hydrocarbons and the inert gas.

Even though my novel oxidation process effects a large increase in the proportion of hydrocarbon oxidized per pass, the unreacted light hydrocarbons remaining still comprise a substantial fraction of the original hydrocarbon feed to the system, and these light hydrocarbons must be recovered. However, the light hydrocarbons boil at very low temperatures and can only be recovered emciently by solvent absorption under pressures of 600 to 1200 pounds per square inch gauge employing very low temperatures of the order of 100 to -40 F.

Accordingly, the mixture of light hydrocarbons and inert gases is compressed by a suitable compressor to the necessary absorption pressure and, after being sufllciently cooled, the mixture is passed through an absorber where the hydrocarbon components are absorbed in a suitable organlc solvent, the unabsorbed inert gases preferably passing upward therein countercurrent to the flow of the absorbing solvent. The absorber solvent is then stripped of the absorbent hydrocarbons and the latter recycled to the oxidation zone, the solvent being again chilled and again circulated through the absorber.

Since the hydrocarbon absorption requires considerable refrigeration in order to effect the removal of the hydrocarbons from the inert gases in an efficient manner at the necessary low temperature, a suitable refrigeration system requiring a considerable power input must be provided. However, the inert gases leaving the hydrocarbon absorber are under rather high pressures and lower than normal temperatures and it is, there fore, an important feature of my novel process to utilize the energy in the inert gases to provide the desired refrigeration as well as to provide the relatively pure oxygen which is employed in effecting the secondary oxidation reaction in my process described above.

Thus, in order to utilize the potential energy contained therein. the inert gases under pressure are allowed to pass through an expander operatively connected to an air compressor. The expansion of and the work performed by the inert gases greatly reduces their temperature while at the same time their expansion causes the air compressor to boost the air from atmospheric pressure to a pressure of 100 to 300 pounds per square inch. The compressed air is then chilled by employing as a refrigerant the low temperature inert gas, and the compressed air is thus liquefied. The liquid air obtained is then fractionated, with the oxygen going to the secondary oxidation reaction zone. The nitrogen which is distilled off is circulated through the system where necessary to provide additional refrigeration to aid in liquefying the compressed air and to aid in chilling the hydrocarbon gas absorption solvent and in chilling the light hydrocarbon gas absorber.

Referring now to the drawing wherein there is shown a preferred embodiment of apparatus for carrying out the novel process of my invention. the gaseous hydrocarbons to be oxidized enter a reactor I under pressure through an inlet ill line I which passes through a heat exchanger I where said gases are preheated. The preheated hydrocarbon gases pass upward in the reactor l and meet a stream of air entering through an inlet 4. The amount of air relative to the entering hydrocarbon is closely controlled. The initial oxidation reaction takes place in a reaction zone comprising a tube 5 and the gaseous reaction mixture leaves reactor I and reaction tube 5 through a product discharge outlet 5'. The oxygen in the reacting mixture is partially consumed by the time the reaction gases reach discharge outlet 5 and the nitrogen present acts as a retarding agent. To effect the desired secondary reaction, oxygen is admitted to outlet 5' through a pipe 6 in an amount controlling the temperature rise desired. The secondary oxidation reaction takes place in a suitable mixing chamber 6' and, following the secondary reaction, the reaction mixture produced is immediately cooled below reaction temperature in heat exchanger 3 by the cooling effect of the entering hydrocarbon gas feed moving countercurrently to the flow of the reaction gases. The cooled reaction gases then pass to a scrubber I which is held at a willciently high temperature to permit removal of any tars and resins produced while the latter are in a liquid form. The temperature of the gaseous reaction mixture is cooled further in cooler B and excess high boiling products are removed in a scrubber 8.

The gaseous reaction mixture now remaining is then passed upward through an absorber Ill countercurrent to a stream of water entering through an inlet II and the water-soluble compounds present are removed, the aqueous solution of water-soluble products which forms being discharged through a line I! at the base of absorber Ill. The temperature in absorber lll is controlled by an internal cooling coil l3. After removal of the water-soluble products the gaseous reaction mixture is then passed through a conduit ll into a second absorber l5 where the cracked, aromatic or unsaturated hydrocarbon gases are removed employing a suitable solvent, which preferably contains some diethylene glycol to ensure the removal of any water and prevent precipitation of the same in the form of ice when the gases are subsequently cooled. The solvent enters absorber I! through a line 16 and flows downwardly in the absorber. The solution formed is discharged at the base of absorber l5 through a discharge pipe II. The absorbed hydrocarbons may be stripped from the solvent and may be oxygenated at low pressure and temperature with the aid of suitable catalysts or may be recycled to reactor l in whole or in part. The unabsorbed gases now remaining consist of light hydrocarbons and inert gas. such as nitrogen.

In order that the process be economically feasible, as stated above, the light hydrocarbons must be recovered, and solvent absorption at low temperatures and high pressures offers the most efflcient means for recovery of these light hydrocarbons.

Accordingly, the gaseous mixture of light hydrocarbons and inert gas is fed through a conduit ll to a compressor is where the pressure is boosted to 600 to 1200 pounds per square inch. The temperature of the gases rises considerably when compressed and the temperature is substantially reduced by means of coolers 20 and H, a suitable cooling medium being employed, which medium is passed through pipe 22. The cooled, compressed gases pass through line 23 into absorber 24 and the light hydrocarbons are absorbed by a stream of cold oil entering absorber 24 through an inlet 25. The absorber oil is chilled in cooler 28 prior to entering absorber 24 and the tem- Derature in said absorber 24 is maintained at the desired low level by the action of a cooling coil 21. The cold oil solution of light hydrocarbons formed leaves absorber 24 through a discharge pipe 28 and is circulated through cooler 2| to reduce the temperature of the compressed gaseous mixture entering absorber 24 to be stripped of its light hydrocarbon content. The oil solution of light hydrocarbons leaves cooler 2i through pipe 29 and may be stripped of the light hydrocarbons in a suitable stripping still (not shown) and the absorber oil recycled through cooler 28 to absorber 24 to absorb additional light hydrocarbons.

The chilled, unabsorbed inert nitrogen gas comes overhead from absorber 24 through a line 30 under high pressure and is passed through an expander 3!. The expansion of the inert nitrogen gas drives an air compressor 22 which draws air in through a line 23 provided with a filter 3. The compressed air passes through an after-cooler through a line 38 provided with a suitable circulating refrigerant, and the chilled air then scrubbed and dehydrated in a scrubber 31. The cooled scrubbed and dehydrated compressed air is then liquefied in heat exchanger 38 by the cold. expanded nitrogen gases leaving expander II. The nitrogen gas is at a temperature of 350 to 250 F. after expansion, at which temperature air at 100 to 300 pounds per square inch gauge may be readily liquefied. The cold nitrogen enters heat exchanger 38 through a pipe 29 and after liquefying the air is passed through cooling coil 21.

The liquid air produced enters fractionating still 4|! through a line 4| where the nitrogen is dstilled ofi' overhead. The nitrogen is piped to heat exchanger 38 through line 42 where it serves to aid in the liquefaction of the compressed air. The purifled liquid oxygen is removed from the base of still through line 43. The oxygen may be employed directly'for the secondary oxidation reaction or may be employed to provide any necessary refrigeration in the system prior to being passed to the oxygenation reaction.

My novel process enables the oxidation of hydrocarbons to valuable products to be conducted efficiently with reduced equipment costs. minimizes expensive heating and cooling operations and reduces the amount of by-products in the eflluent gases which are not economical to recover.

It is to be understood that the foregoing detailed description is given merely by way of illustration and that many variations may be made therein without departing from the spirit of my invention.

Having described my invention, what I desire to secure by Letters Patent is:

1. In a process for the partial oxidation of hydrocarbons in the vapor phase at elevated temperature and pressure to form oxygenated organic compounds, the steps which comprise subjecting the hydrocarbons to an initial partial oxidation with oxygen containing an inert gaseous diluent under such conditions that a temperature of 600 to 900 F. is developed and maintained and then subjecting the gaseous reaction mixture obtained to further oxidation with added oxygen free 01' any inert diluent, said 6 further oxidation producing a temperature higher than that 01 the initial partial oxidation reaction whereby both a partial cracking of unreacted hydrocarbons present and the formation of additional oxygenated organic compounds is efl'ected.

2. In a process for the partial oxidation of hydrocarbons in the vapor phase at elevated temperature and pressure to form oxygenated organic compounds, the steps which comprise subjecting the hydrocarbons to an initial partial oxidation with oxygen containing an inert gaseous diluent at a temperature of 600 to 900 F. and then subjecting the gaseous reaction mixture obtained to further oxidation with added oxygen free of any inert diluent, said further oxidation producing a temperature higher than that of the initial partial oxidation reaction whereby both a partial cracking of unreacted hydrocarbons present and the formation of additional oxygenated organic compounds is effected.

3. In a process for the partial oxidation of hydrocarbons in the vapor phase at elevated temperature and pressure to form oxygenated organic compounds. the steps which comprise subjected the hydrocarbons to an initial partial oxidation with oxygen containing an inert gase ous diluent at a temperature of 600 to 900 F. and then subjecting the gaseous reaction mixture obtained to further oxidation with added oxygen free of any inert diluent, said further oxidation producing a temperature of 900 to 1250 F. whereby both a partial cracking of unreacted hydrocarbons present and the formation of additional oxygenated organic compounds is effected. v

4. In a process for the partial oxidation of hydrocarbons in the vapor phase at elevated temperature and pressure to form oxygenated organic compounds, the steps which comprise subjecting the hydrocarbons to an initial partial oxidation with oxygen containing an inert gaseous diluent at a temperature-of 600 to 900 F. and a pressure of to 200' poundsper square inch gauge and then subjecting the gaseous reaction mixture obtained to further oxidation with added oxygen free of any inert diluent, said further oxidation producing a temperature of 900 to 1250 F. whereby both a partial cracking of unreacted hydrocarbons present and the formation of additional oxygenated organic compounds is effected.

5. In a process for the partial oxidation of hydrocarbons in the vapor phase at elevated temperature and pressure to form oxygenated organic compounds, the steps which comprise subiecting the hydrocarbons to an initial partial oxidation with oxygen containing nitrogen as an inert gaseous diluent at a temperature of 600 to 900 F. and a pressure of 75 to 200 pounds per square inch gauge and then subjecting the gaseous reaction mixture obtained to further oxidation with added oxygen free of any inert diluent, said further oxidation producing a temperature of 900 to l250 F. whereby both a partial cracking of unreacted hydrocarbons present and the formation of additional oxygenated organic compounds is eiiected.

8. Process for the partial oxidation of hydrocarbons in the vapor phase at elevated temperature and pressure to form oxygenated organic compounds, which comprises subjecting the hydrocarbons to an initial partial oxidation in a reaction zone with oxygen containing an inert gaseous diluent under such conditions that a 7 temperatureoimtoeoil'liisdevelopedand maintained, subjecting the gaseous reaction mixture obtained to further oxidation with added oxygen tree 01' any inert diluent, said further oxidation producing a temperature higher than that of the initial partial oxidation reaction whereby both a partial cracking oi unreacted hydrocarbons present and the formation of additional oxygenated organic compounds is eiiected. organic compounds from the reaction gases, separating the unreacted light hydrocarbons lrom the inert gaseous diluent present by absorption under pressure with the aid or a liquid solvent. expanding the unabsorbed inert gaseous diluent to lower the temperature the same and simultaneously to compress air, cooling and liqueiying the compressed air with the aid oi the cooled, expanded inert gaseous diluent, separating the oxygen irom the liquefied air and cycling it to the oxidation reaction zone to eilect further oxidation of the partially oxidized hydrocarbon mixture. and cyoyling the cooled nitrogen separated from the liquefied air to supply necessary refrigeration to the reaction system.

'1. Process tor the partial oxidation of hydrocarbons in the vapor phase at elevated temperature and pressure to form oxygenated organic compounds, which comprises subiecting the hydrocarbons to an initial partial oxidation in a reaction zone with oxygen containing an inert gaseous diluent at a temperature of 600 to 900' R, subjecting the gaseous reaction mixture obtained to further oxidation with added oxygen free of any inert diluent, said further oxidation producing a temperature higher than that of the initial partial oxidation reaction whereby both a partial cracking of unreaeted hydrocarbons present and the formation of additional oxygenated organic compounds is eflected, separating the oxygenated organic compounds from the reaction gases, separrting the unreacted light hydrocarbons from the inert gaseous diluent present by absorption under pressure with the aid oi. a liquid solvent, expanding the unabsorbed inert gaseous diluent to lower the temperature 0! the same and simultaneously to compress air. cooling and liqueiying the compressed air with the aid of the cooled, expanded inert gaseous diluent, separating the oxygen from the liquefied air and cycling it to the oxidation reaction zone to eilect further oxidation oi the partially oxidized hydrocarbon mixture, and cycling the cooled nitrogen separated irorn the liqueiied air to supply necessary refrigeration to the reaction system.

8. Process for the partial oxidation of hydrocarbons in the vapor phase at elevated temperature and pressure to form oxygenated organic compounds, which comprises subjecting the hydrocarbons to an initial partial oxidation in a reaction zone with oxygen containing an inert gaseous diluent at a temperature of 600 to 900" F., subjecting the gaseous reaction mixture obtained to further oxidation with added oxygen free of any inert diluent, said further oxidation producing a temperature of 900 to 1200' F. whereby both a partial cracking or unreacted hydrocarbons present and the formation of additional oxygenated organic compounds is eflected, separating the oxygenated organic compounds from the reaction gases, separating the unreacted light hydrocarbons from the inert gaseous diluent present by absorption under pressure with the aid of a liquid solvent. expanding the unabsorbed inert gaseous diluent to lower the temperature of the same and simultaneously to compress air. cooling and iiqueiying the compressed air with the aid of the cooled, expanded inert gaseous diluent, separating the oxygen from the liquefied air and cycling it to the oxidation reaction zone to eiiect further oxidation 0! the partially oxidized hydrocarbon mixture, and cycling the cooled nitrogen separated from the liquefied air to supply necessary refrigeration to the reaction system.

9. Process for the partial oxidation of hydrocarbons in the vapor phase at elevated temperature and pressure to form oxygenated organic compounds, which comprises subjecting the hydrocarbons to an initial partial oxidation in a reaction zone with oxygen containing an inert gaseous diluent at a temperature 0! 600 to 900 1''. and a pressure oi to 200 pounds per square inch gauge. subjecting the gaseous reaction mixture obtained to further oxidation with added oxygen tree of any inert diluent, said further oxidation producing a temperature of 900 to 1200 F. whereby both a partial cracking of unreacted hydrocarbons present and the formation of additional oxygenated organic compounds is eflected, separating the oxygenated organic compounds from the reaction gases, separating the unreacted light hydrocarbons from the inert gaseous diluent present by absorption under pressure with the aid of aliquid solvent, expanding the unabsorbed inert gaseous diluent to lower the temperature or the same and simultaneously to compress air, cooling and liquefying the compressed air with the aid of the cooled, expanded inert gaseous diluent, separating the oxygen from the liquefied air and cycling it to the oxidation reaction zone to eil'ect further oxidation of the partially oxidized hydrocarbon mixture, and cycling the cooled nitrogen separated from the liquefied air to supply necessary refrigeration to the reaction system.

i0. Process for the partial oxidatlton of hydrocarbons in the vapor phase at elevated temperature and pressure to form oxygenated organic compounds. which comprises subjecting the hydrocarbons to an initial partial oxidation in a reaction zone with oxygen containing an inert gaseous diluent at a temperature of 600 to 900 F. and a pressure of 75 to 200 pounds per square inch gauge, subjecting the gaseous reaction mixture obtained to further oxidatiton with added oxygen free of any inert diluent, said further oxidation producing a temperature or 900 to 1200 F. whereby both a partial cracking of unreacted hydrocarbons present and the formation of additional oxygenated organic compounds is effected, separating the oxygenated organic compounds from the reaction gases, separating the unreacted light hydrocarbons from the inert gaseous diluent present by absorption under a pressure of 600 to 1200 pounds per square inch gauge with the aid of a liquid solvent, expanding the unabsorbed inert gaseous diluent to lower the temperature of the same and simultaneously to compress air, cooling and liquefying the compressed air with the aid of the cooled, expanded inert gaseous diluent, separating the oxygen from the liquefied air and cycling it to the oxidation reaction zone to eii'ect iurther oxidation or the partially oxidized hydrocarbon mixture and cycling the cooled nitrogen separated from the liquefied air to supply necessary refrigeration to the reaction system.

MEINHARD H. KOTZEBUE.

(BeIerenoea on following page) D mmmmces men Number The following references are of record in the file of this patent:

UNITED STATES PATENTS 5 Number Name Date Number 1,959,587 James May 24, 1932 290,613 1,870,816 Lewis Aug. 9. 1932 321,494

Name Date Bludworth et a]. June 19, 1934 James Feb. 27, 1945 FOREIGN PATENTS Country Date Great Britain Nov. 5. 1929 Greet Britain Nov. 14, 1929 

8. PROCESS FOR THE PARTIAL OXIDATION OF HYDROCARBONS IN THE VAPOR PHASE AT ELEVATED TEMPERATURE AND PRESSURE TO FORM OXYGENATED ORGANIC COMPOUNDS, WHICH COMPRISES SUBJECTING THE HYDROCARBONS TO AN INITIAL PARTIAL OXIDATION IN A REACTION ZONE WITH OXYGEN CONTAINING AN INERT GASEOUS DILUENT AT A TEMPERATURE OF 600 TO 900* F., SUBJECTING THE GASEOUS REACTION MIXTURE OBTAINED TO FURTHER OXIDATION WITH ADDED OXYGEN FREE OF ANY INERT DILUENT, SAID FURTHER OXIDATION PRODUCING A TEMPERATURE OF 900 AND 1200*F. WHEREBY BOTH A PARTIAL CRACKING OF UNREACTED HYDROCARBONS PRESENT AND THE FORMATION OF ADDITIONAL OXYGENATED ORGANIC COMPOUNDS IS EFFECTED, SEPARATING THE OXYGENATED ORGANIC COMPOUNDS FROM THE REACTION GASES, SEPARATING THE UNREACTED LIGHT HYDROCARBONS FROM THE INERT GASEOUS DILUENT PRESENT BY ABSORPTION UNDER PRESSURE WITH THE AID OF A LIQUID SOLVENT, EXPANDING THE UNABSORBED INERT GASEOUS DILUENT TO LOWER THE TEMPERATURE OF THE SAME AND SIMULTANEOUSLY TO COMPRESS AIR, COOLING AND LIQUEFYING THE COMPRESSED AIR WITH THE AID OF THE COOLED, EXPANDED INERT GASEOUS DILUENT, SEPARATING THE OXYGEN FROM THE LIQUEFIED AIR AND CYCLING IT TO THE OXIDATION REACTION ZONE TO EFFECT FURTHER OXIDATION OF THE PARTIALLY OXIDIZED HYDROCARBON MIXTURE, AND CYCLING THE COOLED NITROGEN SEPARATED FROM THE LIQUEFIED AIR TO SUPPLY NECESSARY REFRIGERATION TO THE REACTION SYSTEM. 